In many situations a light source is desired to provide a collimated beam of light. The typical method of providing such a collimated beam of light is to utilize a parabolic reflector. Two disadvantages exist in the use of parabolic reflectors, however. One disadvantage relates to the size of a parabolic reflector. If the light source is to have a large aperture, a parabolic reflector must be relatively deep, and thus enclose a large volume. This is particularly true if the parabolic reflector has a relatively short focal length. In situations where space is limited, such as automobile taillights or back-lit displays, the size of such reflectors can be a significant disadvantage.
A second disadvantage lies in the existence of "hot" spots in the light pattern produced by a parabolic reflector. Such hot spots arise from the fact that the parabolic reflector is more efficient at gathering light near the center than at the edges. A parabolic reflector, thus, is not optimum for use in a light source where a uniform intensity is desired.
One alternative to the use of a parabolic reflector is shown in U.S. Pat. No. 4,789,921, commonly assigned herewith. In the approach shown in that application a reflector has Fresnel structures that cause the reflector to have the properties of a parabolic reflector when it is formed into the shape of a cone. That approach allows a reflector to be less deep than the equivalent conventional parabolic reflector, but does not solve the problem of providing a uniform intensity over the entire light source.